Milking of an animal is effected by means of a claw having attached thereto cups which are connected to the animals teats. In the mechanised situation which exists in a milking installation, a milk line connects to the claw to receive the milk. In order to draw off the milk, a constant vacuum of about 0.5 Bar is applied to the milk line, switchable on and off by a valve. The vacuum is switched on prior to commencement of milking and connects the cups to the teats. After milking has been completed, the vacuum is switched off. A second vacuum system provides a pulsating vacuum to the outside of the liners, to stimulate milk flow and maintain blood circulation in the teats. It will be understood, therefore, that in the environment of a milking installation, there are generally available two sources of vacuum namely a constant or steady vacuum and a pulsating vacuum.